1. The Field of the Invention
The present invention relates to electrosurgical devices for ablating tissue in an arthroscopic procedure. More specifically, the present invention relates to electrosurgical devices with an electrode that defines a lumen for aspirating gasses and debris.
2. The Relevant Technology
An arthroscope is an instrument used to look directly into a surgical site. Typically, the arthroscope utilizes a magnifying lens and coated glass fibers that beam an intense, cool light into the surgical site. A camera attached to the arthroscope allows the surgeon to view the surgical site on a monitor in the operating room. With the arthroscope, the surgeon can look directly into a surgical site, such as a knee or shoulder, to diagnose injury and decide on the best treatment. While viewing the surgical site with the arthroscope, the surgeon can repair an injury using a separate surgical instrument.
The ability to view the surgical site in this manner allows for a minimally invasive procedure. In recent years, arthroscopic surgeries have been developed for surgical procedures that traditionally were once very complicated and time consuming. Many of these surgeries are now performed as outpatient procedures using arthroscopic techniques.
At the beginning of the arthroscopic procedure, the patient receives an anesthetic. After the patient has been sufficiently anesthetized, the surgeon makes a plurality of incisions, known as portals. The portals extend from the exterior of the body of the patient to the surgical site. Three portals are usually made: a first for the arthroscope, a second for the surgical instrument, and a third to permit fluids to escape from the surgical site.
Sterile fluid is generally introduced by way of the arthroscope through the first portal. The sterile fluid serves among other purposes to expand the area of the surgical site. The insertion of sterile fluid makes it easier to see and work inside the body of the patient at the surgical site.
Electrosurgical instruments are a common device used in arthroscopy to ablate and/or coagulate tissue. In electrosurgery, an electrode is used to direct a high frequency current near or through body tissue. The high frequency current generates enough heat to ablate tissue. In monopolar electrosurgery the return electrode is a patch placed on the person. Energy that dissipates into the tissue connects the circuit by passing through the patch.
In a bipolar electrosurgical device, the return electrode is placed in a separate location on the electrosurgical device. Energy leaving the ablator electrode passes through fluids and/or tissue and returns to the electrode on the electrosurgical device.
In both monopolar and bipolar electrosurgery, an electrode transfers energy to the surrounding fluid. The energy can be controlled to simply warm the adjacent tissue or it can be used to cut or ablate tissue. Warming tissue is often done to facilitate coagulation. The heating event causes coagulation and thus can be used to stop bleeding in an arthroscopic procedure.
To ablate tissue, larger amounts of energy are applied to the electrode. The electrode generates enough heat to create gas bubbles around the electrode. The gas bubbles have a much higher resistance than tissue or saline, which causes the voltage across the electrode to increase. Given sufficient power the electrode discharges (i.e. arcs). The high voltage current travels through the gas bubbles and creates a plasma discharge. Moving the electrode close to tissue causes the plasma layer to come within a distance sufficiently close to vaporize and ablate the tissue.
The contours and surface area of an electrode are important for controlling where arcing occurs on the electrode and how much power is required to cause a discharge. Current density is greatest at sharp edges. Arcing, and thus ablating, can be controlled by forming electrodes or electrode edges with small surface areas.
Even though gas bubbles can be a necessary or unavoidable consequence of electrosurgery, gas bubbles can pose a problem for the practitioner using arthroscopy. Bubbles formed by an electrosurgical device can block the physician's view in the arthroscopic camera. Thus, bubbles collecting in the surgical site can significantly slow down the surgical procedure or increase the risk that a physician will make an undesirable cut.
To overcome the disadvantages created by bubbles formed in the surgical area, recent electrosurgical devices have been created that have lumens for aspirating gasses and tissue debris. One problem with these electrosurgical devices, however, is that they can become plugged. In operation, an electrosurgical device creates tissue fragments. These tissue fragments are drawn to the opening of the aspirating lumen and can block the passage of gasses. Some recent electrosurgical devices place electrodes above the opening of the lumen to ablate tissue blocking the opening. However, even with these electrodes, there is a period of time when the electrode is breaking down the fragment that gasses cannot pass through. When this event occurs, a surgeon has to wait for the fragment to degrade and pass before the surgeon can continue with the surgical procedure.
Therefore, what is needed is an improved electrosurgical device that can aspirate tissue fragments without disrupting the aspiration of gasses, such that a surgeon's field of vision remains clear.